[Juha]

Hello Christer
The use of graphs made it easy to understand for example by a glance why Spit LF Vs were built, even if its max speed was lower than that of Spit F. V. From graph one sees that in lower altitude the LF V used in the test was clearly faster than the F. V used. Because both a/c used were probably in good condition and were flown by test pilots it is possible to draw a conclusion that also an average LF V is faster at low level than an average F. V and also up to circa what altitude a LF V is faster if both pilots handled their planes more or less same skills. Exact altitude of the transfer is of course only valid to those 2 a/c tested at those conditions were test was made but it also gives a rough estimate for “average” a/c. So those speed graphs give a basis from where one can become add more variables (condition of engine, of airscrew, of skin, plus pilots ability, air temperature etc).

Because this is LW and Axis forum I give the G.50 figures. The max speeds of Fiat G.50s test flown by FAF at 5000m varied between 403 and 430km/h, most important reason to variations was the airscrew used. These tests were flown with 790 mmHg boost pressure not with the max permissible temporary overboost pressure of 890 mmHg but Finns calculated that 430km/h with 790mmHg means circa 445 km/h with 890mmHg. Fiat’s figure for max speed was 484km/h at 5000m. So FAF Fiats were 40 – 60km/h slower that the manufacture claimed. And from a speed graph flown by G.50 FA-31 one sees that the difference to Fiat’s figures was biggest between 2500 – 7000m and smallest around 2000m.
Juha